(a) Technical Field
The present disclosure relates to a liquid crystal display.
(b) Discussion of Related Art
A liquid crystal display (LCD) is one of the most widely used flat panel display devices. The LCD includes a pair of panels including field-generating electrodes such as pixel electrodes and a common electrode, and a liquid crystal (LC) layer interposed between the panels. The LCD generates an electric field in the LC layer by applying voltages to the electrodes, and obtains desired images by controlling the strength of the electric field for determining orientations of LC molecules and polarization of light incident on the LC layer to vary the transmittance of light incident on the LC layer.
The LCD further includes switching elements connected to the pixel electrodes and signal lines such as gate lines and data lines, for applying signals to the switching elements, thereby applying voltages to the pixel electrodes.
Among the LCDs, a vertical alignment (VA) mode LCD, which aligns LC molecules such that the long axes of the LC molecules are perpendicular to the panels in the absence of an electric field, is spotlighted because of its high contrast ratio and wide reference viewing angle. The reference viewing angle means a viewing angle where the contrast ratio is 1:10 or the luminance sequence of grays starts to be reversed.
The wide viewing angle of the VA mode LCD can be realized by cutouts in the field-generating electrodes and protrusions on or under the field-generating electrodes. Since the cutouts and the protrusions can determine the tilt directions of the LC molecules, the tilt directions can be distributed into several directions by using the cutouts and the protrusions so to widen the reference viewing angle.
However, the protrusions and the cutouts obstruct the transmission of incident light and, thus, the light transmittance decreases as the number of the protrusions or the cutouts increases. In order to increase the light transmittance, the area of the pixel electrodes is suggested to be enlarged. However, the suggested configuration makes adjacent pixel electrodes close and makes the pixel electrodes and the data lines adjacent thereto close such that strong lateral electric fields are generated near the edges of the pixel electrodes. The lateral electric fields disorder the orientations of the LC molecules to generate visible texture in the image, as well as light leakage.
In addition, the VA mode LCD has poor lateral visibility as compared with front visibility. For example, in a conventional LCD provided with cutouts, the image becomes brighter toward the lateral edges of the LCD and, in a severe case, the luminance difference between high grays vanishes to make the overall image dim.
To improve the lateral visibility, a pixel is divided into two subpixels capacitively coupled to each other. One of the two subpixels is directly supplied with a voltage, while the other is subjected to a voltage drop by the capacitive coupling, such that the two subpixels have different voltages to result in different light transmittances.